The present invention relates to a tire with radial carcass reinforcement furthermore comprising a reinforcement formed of at least one ply of reinforcement elements which is composed of wires or cables forming an angle of between 0.degree. and 15.degree. with the circumferential direction of said tire. It also relates to the method of production of said ply from a strip of wires and/or cables.
In the case of a tire for a passenger vehicle, the ply or plies of circumferential elements are generally crown reinforcement plies of continuous polyamide cables, and in particular aliphatic polyamide, these cables permitting a certain elasticity while permitting, owing to their property of contractility under the action of heat, major hooping of the subjacent plies, which are generally of metal and formed of cables forming a certain angle, generally between 10.degree. and 45.degree., with the circumferential direction.
This type of textile cable is not recommended for use in large quantities in crown reinforcements for "heavy-goods vehicle" tires, in particular for so-called highway tires. In fact, the afore-mentioned material gives rise to heating, which is incompatible with a long life of the crown of the tire. The use of metal cables is preferable, because firstly it results in a lower production of heat in the zones subject to heating, and secondly results in better dissipation of the heat produced.
The use of substantially circumferential metal cables in a crown reinforcement ply for a "heavy-goods vehicle" tire is not without its problems, in particular in the molding of the tire in the vulcanization mold. Good distribution of the rubber mix of the tread when the curing press is closed and vulcanization begins requires the tire, in the non-vulcanized state, to have a tread diameter, measured in the equatorial plane, which is slightly less than the diameter, measured under the same conditions, which it has to have in the vulcanization mold, and to be subjected to what is customarily called additional shaping in the vulcanization mold. A crown reinforcement for a tire with radial carcass reinforcement, comprising one or more plies of continuous, inextensible metal cables (that is to say those having an elongation of less than 0.2% under a tensile force equal to 10% of the breaking load), makes said additional shaping under low tension possible only with great difficulty or not at all.
The use, as described for example in patent FR 2 013 812, of inextensible metal cables which are discontinuous over a circumferential length has then proved judicious, firstly because it permits sufficient elasticity of the ply in the non-vulcanized state, and secondly because it permits the obtention in the vulcanized state of a modulus of elasticity in tension of the ply which is very largely sufficient, said modulus being obtained by judicious selection of the length, whether variable or not, of the cut cables and by the circumferential offset of the cuts.
The elasticity of the non-vulcanized ply is not only sufficient but too great for ready handling during production of the tire, and has proved to be the cause of laying irregularities, and in particular irregularities in the diameters of crown reinforcements for the various tires of one and the same series.
It is obvious that the problem occurs in the same way with any reinforcement which comprises metal cables, the lengths of which are less than the circumferential lengths of the parallel ones occupied in the tire, insofar as it has been prepared independently of the building drum and/or shaping drum for the non-vulcanized blanks of tire carcass reinforcements, without however inevitably having the same consequences.